Various types of computers use touch screens to receive input from end-users. Generally, an end-user uses a finger or other instrument to make physical contact with the touch screen. The computer coupled to the touch screen detects the physical contact and reacts accordingly.
In some cases, triangulation techniques may be used to pinpoint the precise location of a touch on a touch screen. Specifically, a group of light detectors may be arranged along the perimeter of a touch screen, while a pair of light emitters is arranged in two corners of the touch screen. The light emitters emit light across the plane of the touch screen. When a user's finger touches the touch screen, at least part of the light emitted from each of the light emitters is obstructed. These obstructions of light are detected by the light detectors. Triangulation analysis may be performed to determine the location at which the obstructed areas intersect. This intersection point is determined to be the finger's location.
This approach may work well for single-finger touches. However, if a user tries to use multiple fingers on the touch screen, triangulation becomes difficult. For example, a user may try to use two fingers on the touch screen. Each finger touch results in two light-obstructed areas (one light-obstructed area per light emitter). Thus, two finger touches result in four light-obstructed areas. The four light-obstructed areas intersect with each other at four points. Two of these points represent the locations of the actual fingers on the touch screen. However, the remaining two intersection points are merely “phantom” touch points, since they indicate that fingers are touching the screen at those points when, in reality, they are not. A reliable technique for distinguishing phantom touch points from actual touch points is desirable.